As known, motor vehicles have a front frame accommodated in the front engine compartment and designed so as to obtain an adequate degree of safety, in particular for the passengers in the passenger compartment, in the event of accidents with front impact.
In particular, the front frame is provided with at least one pair of side-members, connected at their front ends to a bumper and having collapsible zones to absorb energy due to impacts at relatively high speed. In the event of front impact against an obstacle arranged approximately at the centreline of the motor vehicle, the above-mentioned collapsible zones allow an excellent degree of safety to be obtained in the passenger compartment. Nevertheless, when the front impact occurs with an offset, that is with a misalignment with respect to the longitudinal centreline axis, and concerns only a front edge of the motor vehicle, it is expedient to provide additional safety precautions in order to comply with the safety requirements established by the regulations. In particular, said regulations provide safety tests with impacts where there is a so-called “small overlap” (for example equal to 25%) between the motor vehicle and the obstacle during the impact. In these cases, the stresses due to the impact are only unloaded onto one side of the motor vehicle, but the plastic deformation of said side of the frame is not sufficient to absorb all the impact energy, and therefore the passenger compartment is subject to deformations which instead should be avoided to ensure the safety of the passengers.
Some solutions (such as the one shown in the patent application EP2927097, corresponding to the preamble of claim 1) include a safety device with a beam which is arranged beside at least one of the two side-members and which, during the impact, acts as a strut to cause a lateral thrust on the powertrain unit, that is in a transverse direction, towards the side opposite the one subject to the impact, so as to exploit the inertia of the powertrain unit and therefore cause the motor vehicle to move away from the obstacle during the impact. This deviation of the entire motor vehicle in a sideways direction is extremely advantageous for maintaining substantially intact the part of body defining the passenger compartment.
In the known solutions of the just described type, however, the behaviour is not always uniform and does not always correspond to the design specifications.
In fact, it should be borne in mind that, for the same type of motor vehicle and engine compartment, powertrain units are often installed with shapes and dimensions slightly different from each other, that is powertrain units with engines having different displacements and/or with different transmissions (automatic or manual, for example). This difference generally results in a variation in spaces and overall dimensions in the areas where the above-mentioned safety device operates during the impact. Consequently, said variation in spaces and overall dimensions causes a variation in the response times of the thrust on the powertrain unit and therefore of the dynamic behaviour of the motor vehicle during the impact.
Furthermore, even considering one single type of powertrain unit installed in the engine compartment, if the same safety device is mounted on the two sides of the motor vehicle, generally a different dynamic behaviour is noted when the impact occurs with “small overlap” on the right or left, since the position of the powertrain unit is not perfectly centred in the engine compartment and/or the overall dimensions at its opposite lateral ends are different from each other.
The need is therefore felt to provide expedients such as to obtain a more uniform behaviour in dynamic impact conditions with variation in the shape and dimensions of the powertrain unit in the engine compartment and with variation in the side (right or left) on which the frontal impact occurs.
Furthermore, the need is felt to obtain a more effective solution as regards reduction of the response times in the sideways movement caused by the safety beam on the powertrain unit during the impact with “small overlap”.